CN110649896A - Multi-band analog predistortion circuit applied to wireless communication - Google Patents

Abstract

The invention discloses a multi-band analog predistortion circuit applied to wireless communication, which belongs to the technical field of electronic information. This solution not only effectively solves the problem that the traditional linearizer has a narrow bandwidth and can only achieve linearization in a certain frequency band, but also ensures that the port VSWR and isolation are good in multiple frequency bands that need to be linearized. The problems of narrow bandwidth, poor isolation and standing wave characteristics of traditional linearizers are solved. The present invention can realize linearizers with dual-band, triple-band or even more frequency bands, which can greatly reduce circuit size and production cost. Has a very good application prospect.

Description

A Multi-band Analog Predistortion Circuit Applied in Wireless Communication

technical field

The invention belongs to the technical field of electronic information, and is a multi-band analog predistortion circuit which can be applied to wireless communication.

Background technique

With the development of science and technology, the contemporary communication industry has undergone great changes. In the past, satellite transmissions were all single-carrier video signals, and the generation of digital compression technology allows multi-carrier signals to be transmitted in the same frequency band. Mobile phones and Internet services have changed the traditional satellite loading, and new terrestrial microwave transmission services for video services, data transmission, mobile phones, and personal communications have appeared one after another, and the use of complex modulation techniques has become more and more common.

In order to complete higher quality data transmission, efficient and complex modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) and Quadrature Amplitude Modulation (such as 64QAM) are often used. High peak-to-average ratio (PAPR), which will inevitably require some components in the system to have a large linear dynamic range; the final stage wave power amplifier in the system often works in a saturated state, resulting in nonlinear distortion, which deteriorates the wireless communication system. Therefore, this type of technology has higher requirements on the linearity of the final power amplifier. At present, millimeter-wave wireless communication systems have more and more stringent requirements on the linearity of traveling wave tube power amplifiers and solid-state power amplifiers. All in all, the research of millimeter-wave power amplifier linearization technology is of great significance to the millimeter-wave wireless communication system and even the entire wireless communication field.

The literatures "New Ka-band Analog Predistortion Linearizer" and "C-band Predistortion Linearizer with 90° Branch Bridge" both use reflective linearization architectures. The bias voltage of the diodes at the straight end and the coupling end can change the reflection coefficient of the circuit, so that the nonlinear signal caused by it is reflected by the straight end and the coupling end, and then combined and output at the isolated end. Since the quadrature coupler used in this architecture is designed based on quarter-wavelength, it is a narrow-band device. When the input signal frequency deviates from the center frequency, the characteristic impedance and phase characteristics of the coupler will change, so that a certain degree of The bandwidth of the linearizer is limited, and the input VSWR and isolation are degraded. In addition, the bias circuit of the diode is also designed with a quarter wavelength, which limits the bandwidth of the linearizer to a certain extent. If predistortion is required in multiple frequency bands, a combination of multiple linearizers is required. This increases circuit size, adjustment difficulty, and fabrication cost.

Most of the current reflective linearizers and two-way vector synthesis linearizers use a 90° bridge as the core component, so the current linearizers in the millimeter-wave band are very narrow in bandwidth, and can only pre-process a single specific frequency band. Distortion compensation.

SUMMARY OF THE INVENTION

The invention introduces the idea of multi-band, and proposes a multi-band analog pre-distortion circuit based on the traditional analog pre-distortion circuit, so as to achieve linearization of multiple passbands in a wider frequency range.

The invention replaces the traditional single-frequency coupler and bias circuit by adopting the dual-frequency branch line coupler and the multi-sector feeding network, so that the linearizer has the function of multi-band linearization, and the frequency interval of the multi-band can reach several G and above.

The technical solution of the present invention is a multi-band analog predistortion circuit applied to wireless communication, the predistortion circuit comprising: a dual-frequency coupler, a first capacitor (C1), a second capacitor (C2), and a current limiting resistor (R1) , the first diode (D1), the second diode (D2), the radio frequency choke coil (L1);

The dual-frequency coupler includes: a total of 8 square microstrip lines from the first to the eighth with the same structure located in the same plane, wherein the first microstrip line, the fourth microstrip line, and the seventh microstrip line are connected in sequence , and are located on the same line; the third microstrip line, the fifth microstrip line, and the eighth microstrip line are connected in sequence and located on the same line; the common node of the first and fourth microstrip lines is the same as the third and fifth microstrip lines. The common contacts of the strip lines are connected by a second microstrip line, the common nodes of the fourth and seventh microstrip lines and the common contacts of the fifth and eighth microstrip lines are connected by a sixth microstrip line, and the second and fifth microstrip lines are connected by a sixth microstrip line. , 6, and 4 microstrip lines are surrounded by a "mouth"-shaped structure; the common node of the first and fourth microstrip lines is the input end (M1) of the dual-frequency coupler, and the third and fifth microstrip lines are The common contact is the isolation end (M2) of the dual-frequency coupler, the common node of the fourth and seventh microstrip lines is the straight-through end (M3) of the dual-frequency coupler, and the common contact of the fifth and eighth microstrip lines is the coupling end (M4) of the dual-frequency coupler;

One end of the first capacitor (C1) is used as the radio frequency input of the predistortion circuit, and the other end is connected to the input end (M1) of the dual-frequency coupler; at the same time, the input end (M1) of the dual-frequency coupler passes through another branch in turn. Connect the RF choke coil (L1), the current limiting resistor (R1) and then the control voltage vcc;

One end of the second capacitor (C2) is used as the radio frequency output of the predistortion circuit, and the other end is connected to the isolation end (M2) of the dual-frequency coupler;

The straight-through end (M3) of the dual-frequency coupler is connected to the input end of the first diode (D1), and the output end of the first diode (D1) is grounded; the coupling end (M4) of the dual-frequency coupler The input terminal of the second diode (D2) is connected, and the output terminal of the second diode (D2) is grounded.

Further, the first, third, seventh and eighth microstrip lines in the dual-frequency coupler are branch lines, the second and sixth microstrip lines are branch lines, and the fourth and fifth microstrip lines are main lines; The calculation methods for the impedance Z ₁ of the branch line, the impedance Z ₂ of the main line, and the impedance Z ₃ of the branch line are:

where Z ₀ is the 50 ohm characteristic impedance, f ₁ is the lower frequency of the desired dual frequency, f ₂ is the higher frequency of the desired dual frequency,

The radio frequency choke coil (L1) and the current limiting resistor (R1) of the present invention constitute the feeding circuit of the linearizer. One function of the feeding network is to provide a DC bias to the diode, so as to adjust the working state of the diode, and another function is to provide a DC bias to the diode. It is to choke the RF signal to prevent the RF signal from entering the DC power supply. After the signal is reflected by the straight end (M3) and the coupling end (M4), it is synthesized and output at the isolation end (M2). By adjusting the feed voltage, the gain and phase shape of the output signal can be changed. The multi-band analog predistortion circuit structure of this invention is shown in Figure 4.

The present invention is a novel circuit design applied to the analog predistortion circuit. The scheme not only effectively solves the problem that the traditional linearizer has a narrow bandwidth and can only achieve linearization within a certain frequency band, but also ensures that the Port standing wave coefficient and isolation in multiple frequency bands are good. The problems of narrow bandwidth, poor isolation and standing wave characteristics of traditional linearizers are solved. The present invention can realize linearizers with dual-band, triple-band or even more frequency bands, which can greatly reduce circuit size and production cost. Has a very good application prospect.

Description of drawings

Fig. 1 Structure of traditional reflective analog predistorter;

Figure 2 π-shaped dual-frequency impedance converter structure;

Fig. 3 multi-band linearizer structure of the present invention;

Figure 4. Gain-phase expansion curve of changing bias voltage at 28GHz;

Figure 5. Gain-phase expansion curve of changing bias voltage at 38GHz;

Fig. 6 is the gain-phase expansion curve of changing the bias voltage vbias at 28GHz;

Fig. 7 is the change curve of the gain and phase expansion of changing the bias voltage vbias at 38GHz.

Detailed ways

The present invention enables the linearizer to have the function of multi-band linearization. Taking the reflection type double-band linearizer as an example, the implementation process of the whole scheme is described. First select a suitable dual-frequency coupler structure. Here, a π-shaped dual-frequency branch line coupler is used for design. The structure is shown in Figure 2.

In this specific embodiment, the resistance value of the impedance line actually manufactured is in the range of 20-120 ohms, and the impedance Z ₁ of the branch line, the impedance Z ₂ of the main line, and the impedance Z ₃ of the branch line are calculated by the following formula;

Select the frequency f ₁ to be 28GHz and f ₂ to be 38GHz, and then calculate δ=0.15, Z ₁ =36.4Ω, Z ₂ =51.5Ω, Z ₃ =105.9Ω. After setting the parameters according to the plate, calculate each microstrip The physical parameters of length and width of line branches are shown in Table 1. The function of the dual-frequency coupler is verified by the schematic diagram simulation of the software ADS (Advanced Design System).

As can be seen from Figure 4, S ₁₁ and S ₄₁ of the dual-frequency coupler are less than -19dB, indicating that the isolation and port standing wave are relatively good, and S ₂₁ and S ₃₁ are 3.3dB and 3.1dB respectively.

Figure 5 shows that the phase difference between the ports at the two frequency bands is about 90°. The results in Fig. 4 and Fig. 5 show that the coupler has two frequency bands simultaneously at f ₁ =28GHz and f ₂ =38GHz, which satisfies the dual-frequency characteristic and realizes the function of the dual-frequency coupler.

The diode adopts MA4E1317, and the plate adopts Rogers 5880 with a thickness of 10 mil. The dual-band analog predistorter is simulated by software ADS.

Figure 6 shows the gain-phase expansion curve of changing the bias voltage vbias at 28GHz. It can be seen that the gain expansion reaches 6.8dB and the phase expansion reaches 41°.

Figure 7 shows the gain-phase expansion curve of changing the bias voltage vbias at 38GHz. It can be seen that the gain expansion reaches 4dB and the phase expansion reaches 40°.

It can be seen from the simulation results that the multi-band linearizer can generate gain and phase expansion in two frequency bands of 28GHz and 38GHz, the frequency band interval is 10GHz, and the gain and phase expansion are large.

Table I

Z₁ Z₂ Z₃ 36.4Ω 51.5Ω 105.9Ω L₁ L₂ L₃ 1.62mm 1.66mm 5.22mm w₁ w₂ w₃ 1.2mm 0.72mm 0.16mm

Claims (2)

1. A multi-band analog predistortion circuit applied to wireless communication, the predistortion circuit comprising: a dual-frequency coupler, a first capacitor (C1), a second capacitor (C2), a current limiting resistor (R1), a first diode (D1), second diode (D2), RF choke coil (L1); The dual-frequency coupler includes: a total of 8 square microstrip lines from the first to the eighth with the same structure located in the same plane, wherein the first microstrip line, the fourth microstrip line, and the seventh microstrip line are connected in sequence , and are located on the same line; the third microstrip line, the fifth microstrip line, and the eighth microstrip line are connected in sequence and located on the same line; the common node of the first and fourth microstrip lines is the same as the third and fifth microstrip lines. The common contacts of the strip lines are connected by a second microstrip line, the common nodes of the fourth and seventh microstrip lines and the common contacts of the fifth and eighth microstrip lines are connected by a sixth microstrip line, and the second and fifth microstrip lines are connected by a sixth microstrip line. , 6, and 4 microstrip lines are surrounded by a "mouth"-shaped structure; the common node of the first and fourth microstrip lines is the input end (M1) of the dual-frequency coupler, and the third and fifth microstrip lines are The common contact is the isolation end (M2) of the dual-frequency coupler, the common node of the fourth and seventh microstrip lines is the straight-through end (M3) of the dual-frequency coupler, and the common contact of the fifth and eighth microstrip lines is the coupling end (M4) of the dual-frequency coupler; One end of the first capacitor (C1) is used as the radio frequency input of the predistortion circuit, and the other end is connected to the input end (M1) of the dual-frequency coupler; at the same time, the input end (M1) of the dual-frequency coupler passes through another branch in turn. Connect the RF choke coil (L1), the current limiting resistor (R1) and then the control voltage vcc; One end of the second capacitor (C2) is used as the radio frequency output of the predistortion circuit, and the other end is connected to the isolation end (M2) of the dual-frequency coupler; The straight-through end (M3) of the dual-frequency coupler is connected to the input end of the first diode (D1), and the output end of the first diode (D1) is grounded; the coupling end (M4) of the dual-frequency coupler The input terminal of the second diode (D2) is connected, and the output terminal of the second diode (D2) is grounded. 2. a kind of multi-band analog predistortion circuit applied to wireless communication as claimed in claim 1 is characterized in that the first, third, seventh and eighth microstrip lines in the dual-frequency coupler are branch lines, The second and sixth microstrip lines are branch lines, and the fourth and fifth microstrip lines are main lines; the calculation methods for the impedance Z ₁ of the branch lines, the impedance Z ₂ of the main line, and the impedance Z ₃ of the branch lines are:

where Z ₀ is the 50 ohm characteristic impedance, f ₁ is the lower frequency of the desired dual frequency, f ₂ is the higher frequency of the desired dual frequency,

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